In the formation of intricate cast shapes of silicon carbide having delicate, thin, complex, curved surfaces, it is desirable to utilize a mold such as plaster of paris which can be conveniently formed by known processes. In employing such a mold it is desirable to use a slip cast technique as described in Fredriksson U.S. Pat. No. 2,964,823. However, the green product formed by slip casting silicon carbide is relatively fragile and, in a complex mold system, it is extremely difficult to remove the mold without harming the green casting or it can be very costly to make a multipiece mold. In the present invention this difficulty is overcome in several ways, preferably by providing in the slip casting mix a water miscible resin which can be cured by firing the mold (and the cast shape) to a relatively low temperature. Alternatively the mold and silicon carbide slip casting are heated to a temperature in excess of about 600.degree. C. for a sufficiently long time to oxidize the silicon carbide and thereby substantially increase the green strength of the casting. Thereafter, the mold and the cured casting are subjected to an acid bath which destroys the plaster of paris in the mold and frees the casting for subsequent treatment. Alternatively, or additionally, the plaster mold may be treated by incorporating in the plaster of paris mold mix 10-15% (by weight) of an aqueous solution which contains about 1 to 5% (by weight) of an organic polymer and the mold is heated in a oxygen-containing atmosphere to a sufficiently high temperature to burn out a substantial portion of the polymer in the mold and thereby drastically weaken the mold to permit its ready removal from the green casting.